diff --git a/src/SpiceSharpParser.IntegrationTests/Examples/Circuits/MosfetExample3.cir b/src/SpiceSharpParser.IntegrationTests/Examples/Circuits/MosfetExample3.cir
new file mode 100644
index 00000000..cae39dda
--- /dev/null
+++ b/src/SpiceSharpParser.IntegrationTests/Examples/Circuits/MosfetExample3.cir
@@ -0,0 +1,5 @@
+Mosfet circuit
+Md 0 1 2 3 my-pmos
+.model my-pmos.1 pmos(level = 49 lmin=0.18u)
+.model my-pmos.2 pmos(level = 49 lmin=1.18u)
+.END
diff --git a/src/SpiceSharpParser.IntegrationTests/Examples/Extensions/Aggregate.cs b/src/SpiceSharpParser.IntegrationTests/Examples/Extensions/Aggregate.cs
new file mode 100644
index 00000000..71dab453
--- /dev/null
+++ b/src/SpiceSharpParser.IntegrationTests/Examples/Extensions/Aggregate.cs
@@ -0,0 +1,48 @@
+using SpiceSharp.Components;
+using SpiceSharp.Entities;
+using SpiceSharp.Simulations;
+using System.Collections.Generic;
+using System.Xml.Linq;
+
+public class BSIM3AggregateModel : Entity
+{
+    /// <summary>
+    /// Gets the models in the aggregate model based on sizes.
+    /// </summary>
+    public HashSet<BSIM3Model> Models { get; } = [];
+
+    /// <summary>
+    /// Creates an aggregate model.
+    /// </summary>
+    /// <param name="name">The name.</param>
+    public BSIM3AggregateModel(string name)
+        : base(name)
+    {
+    }
+
+    /// <summary>
+    /// Creates an aggregate model based on sizes.
+    /// </summary>
+    /// <param name="name"></param>
+    /// <param name="models"></param>
+    public BSIM3AggregateModel(string name, IEnumerable<BSIM3Model> models)
+        : base(name)
+    {
+        foreach (var model in models)
+            Models.Add(model);
+    }
+
+    public override void CreateBehaviors(ISimulation simulation)
+    {
+        throw new System.NotImplementedException();
+    }
+
+    /// <inheritdoc />
+    public override IEntity Clone()
+    {
+        var n = new BSIM3AggregateModel(Name);
+        foreach (var model in Models)
+            n.Models.Add((BSIM3Model)model.Clone());
+        return n;
+    }
+}
\ No newline at end of file
diff --git a/src/SpiceSharpParser.IntegrationTests/Examples/Extensions/ComplexMosfetModelGenerator.cs b/src/SpiceSharpParser.IntegrationTests/Examples/Extensions/ComplexMosfetModelGenerator.cs
new file mode 100644
index 00000000..57ea5929
--- /dev/null
+++ b/src/SpiceSharpParser.IntegrationTests/Examples/Extensions/ComplexMosfetModelGenerator.cs
@@ -0,0 +1,43 @@
+using SpiceSharp.Components;
+using SpiceSharpParser.ModelReaders.Netlist.Spice.Context.Models;
+
+namespace SpiceSharpParser.ModelReaders.Netlist.Spice.Readers.EntityGenerators.Models
+{
+    public class ComplexMosfetModelGenerator : MosfetModelGenerator, ICustomModelGenerator
+    {
+        public ComplexMosfetModelGenerator()
+        {
+        }
+
+        public Context.Models.Model Process(Context.Models.Model model, IModelsRegistry models)
+        {
+
+            if (model.Entity is BSIM3Model bsim3Model)
+            {
+
+                if (model.Name.Contains("."))
+                {
+                    var aggregateName = bsim3Model.Name.Substring(0, bsim3Model.Name.IndexOf('.'));
+                    var aggregate = models.FindModel(aggregateName);
+                    if (aggregate != null)
+                    {
+                        var aggrategeEntity = aggregate.Entity as BSIM3AggregateModel;
+                        aggrategeEntity.Models.Add(bsim3Model);
+
+                        return aggregate;
+                    }
+                    else
+                    {
+                        var aggrategeEntity = new BSIM3AggregateModel(aggregateName);
+                        aggrategeEntity.Models.Add(bsim3Model);
+
+                        return new Context.Models.Model(aggregateName, aggrategeEntity, null);
+                    }
+
+                }
+
+            }
+            return model;
+        }
+    }
+}
\ No newline at end of file
diff --git a/src/SpiceSharpParser.IntegrationTests/Examples/Extensions/CustomMosfetModelTest.cs b/src/SpiceSharpParser.IntegrationTests/Examples/Extensions/CustomMosfetModelTest.cs
index ed0a7c82..6204284c 100644
--- a/src/SpiceSharpParser.IntegrationTests/Examples/Extensions/CustomMosfetModelTest.cs
+++ b/src/SpiceSharpParser.IntegrationTests/Examples/Extensions/CustomMosfetModelTest.cs
@@ -80,6 +80,36 @@ public void When_BSIM1_Used_NoExceptions()
             spiceSharpReader.Settings.Mappings.Components.Map("M", mosfetGenerator);
 
 
+            var spiceSharpModel = spiceSharpReader.Read(parseResult.FinalModel);
+
+            Assert.False(spiceSharpModel.ValidationResult.HasError);
+            Assert.False(spiceSharpModel.ValidationResult.HasWarning);
+        }
+
+        [Fact]
+        public void When_BSIM3_Used_NoExceptions()
+        {
+            // Create a model from text file
+            string path = Path.Combine(Directory.GetCurrentDirectory(), "Examples/Circuits/MosfetExample3.cir");
+            var netlistContent = File.ReadAllText(path);
+            var parser = new SpiceNetlistParser();
+            parser.Settings.Lexing.HasTitle = true;
+            var parseResult = parser.ParseNetlist(netlistContent);
+
+            // Convert to Spice#
+            var spiceSharpReader = new SpiceSharpReader();
+            spiceSharpReader.Settings.CaseSensitivity.IsModelTypeCaseSensitive = false;
+
+            // custom mosfet models
+            var modelGenerator = new ComplexMosfetModelGenerator();
+            modelGenerator.AddGenericLevel<BSIM3Model, SpiceSharpBSIM.Components.Semiconductors.BSIM.BSIM3Behaviors.ModelParameters>(49);
+
+            spiceSharpReader.Settings.Mappings.Models.Map(new[] { "PMOS", "NMOS" }, modelGenerator);
+            var mosfetGenerator = new MosfetGenerator();
+            mosfetGenerator.AddMosfet<SpiceSharp.Components.Mosfet3Model, SpiceSharp.Components.Mosfet3>();
+            spiceSharpReader.Settings.Mappings.Components.Map("M", mosfetGenerator);
+
+
             var spiceSharpModel = spiceSharpReader.Read(parseResult.FinalModel);
 
             Assert.False(spiceSharpModel.ValidationResult.HasError);
diff --git a/src/SpiceSharpParser.IntegrationTests/SpiceSharpParser.IntegrationTests.csproj b/src/SpiceSharpParser.IntegrationTests/SpiceSharpParser.IntegrationTests.csproj
index 95097b93..2b1b40db 100644
--- a/src/SpiceSharpParser.IntegrationTests/SpiceSharpParser.IntegrationTests.csproj
+++ b/src/SpiceSharpParser.IntegrationTests/SpiceSharpParser.IntegrationTests.csproj
@@ -97,6 +97,9 @@
     <None Update="Examples\Circuits\Example04_reversed.cir">
       <CopyToOutputDirectory>Always</CopyToOutputDirectory>
     </None>
+    <None Update="Examples\Circuits\MosfetExample3.cir">
+      <CopyToOutputDirectory>Always</CopyToOutputDirectory>
+    </None>
     <None Update="Examples\Circuits\MosfetExample2.cir">
       <CopyToOutputDirectory>Always</CopyToOutputDirectory>
     </None>
diff --git a/src/SpiceSharpParser/ModelReaders/Netlist/Spice/Readers/EntityGenerators/IModelGenerator.cs b/src/SpiceSharpParser/ModelReaders/Netlist/Spice/Readers/EntityGenerators/IModelGenerator.cs
index 37544c3f..4c4dcff9 100644
--- a/src/SpiceSharpParser/ModelReaders/Netlist/Spice/Readers/EntityGenerators/IModelGenerator.cs
+++ b/src/SpiceSharpParser/ModelReaders/Netlist/Spice/Readers/EntityGenerators/IModelGenerator.cs
@@ -7,4 +7,9 @@ public interface IModelGenerator
     {
         Model Generate(string id, string type, SpiceSharpParser.Models.Netlist.Spice.Objects.ParameterCollection parameters, IReadingContext context);
     }
+
+    public interface ICustomModelGenerator : IModelGenerator
+    {
+        Context.Models.Model Process(Context.Models.Model model, IModelsRegistry models);
+    }
 }
\ No newline at end of file
diff --git a/src/SpiceSharpParser/ModelReaders/Netlist/Spice/Readers/EntityGenerators/StochasticModelsGenerator.cs b/src/SpiceSharpParser/ModelReaders/Netlist/Spice/Readers/EntityGenerators/StochasticModelsGenerator.cs
index dbea6bfe..5d1af38a 100644
--- a/src/SpiceSharpParser/ModelReaders/Netlist/Spice/Readers/EntityGenerators/StochasticModelsGenerator.cs
+++ b/src/SpiceSharpParser/ModelReaders/Netlist/Spice/Readers/EntityGenerators/StochasticModelsGenerator.cs
@@ -82,8 +82,18 @@ public Context.Models.Model GenerateModel(IModelGenerator modelGenerator, string
             RegisterDevAndLotModels(parameters, stochasticModelRegistry, model, (modelId) =>
             {
                 var stochasticCandidate = modelGenerator.Generate(modelId, type, filteredParameters, context);
-                context.ModelsRegistry.RegisterModelInstance(stochasticCandidate);
-                return stochasticCandidate;
+
+                if (modelGenerator is ICustomModelGenerator custom)
+                {
+                    var model = custom.Process(stochasticCandidate, context.ModelsRegistry);
+                    context.ModelsRegistry.RegisterModelInstance(model);
+                    return model;
+                }
+                else
+                {
+                    context.ModelsRegistry.RegisterModelInstance(stochasticCandidate);
+                    return stochasticCandidate;
+                }
             });
             return model;
         }