diff --git a/.changelog.d/767.added b/.changelog.d/767.added
new file mode 100644
index 00000000..2874294e
--- /dev/null
+++ b/.changelog.d/767.added
@@ -0,0 +1 @@
+Lumerical simulations now honor LayerStack sidewall angles through the Layer Builder.
diff --git a/gplugins/lumerical/tests/test_write_sparameters_lumerical.py b/gplugins/lumerical/tests/test_write_sparameters_lumerical.py
index d465ed6e..cdb4bbbf 100644
--- a/gplugins/lumerical/tests/test_write_sparameters_lumerical.py
+++ b/gplugins/lumerical/tests/test_write_sparameters_lumerical.py
@@ -10,6 +10,7 @@
 class _Session:
     def __init__(self) -> None:
         self.ports = 0
+        self.layer_settings: list[tuple[object, ...]] = []
 
     def newproject(self) -> None:
         pass
@@ -32,6 +33,21 @@ def addfdtd(self, **kwargs: object) -> None:
     def gdsimport(self, *args: object) -> None:
         pass
 
+    def addlayerbuilder(self) -> None:
+        pass
+
+    def set(self, *args: object) -> None:
+        pass
+
+    def loadgdsfile(self, *args: object) -> None:
+        pass
+
+    def addlayer(self, *args: object) -> None:
+        pass
+
+    def setlayer(self, *args: object) -> None:
+        self.layer_settings.append(args)
+
     def addport(self) -> None:
         self.ports += 1
 
@@ -76,3 +92,30 @@ def test_keeps_ports_on_layers_not_in_layer_stack(monkeypatch, tmp_path) -> None
 
     assert result is session
     assert session.ports == 2
+
+
+def test_uses_layer_builder_for_sidewall_angle(monkeypatch, tmp_path) -> None:
+    monkeypatch.setitem(sys.modules, "lumapi", ModuleType("lumapi"))
+    component = gf.components.straight(length=10, cross_section="strip")
+    layer_stack = LayerStack(
+        layers={
+            "core": LayerLevel(
+                layer=(1, 0),
+                thickness=0.22,
+                zmin=0,
+                material="sio2",
+                sidewall_angle=10,
+            )
+        }
+    )
+    session = _Session()
+
+    write_sparameters_lumerical(
+        component,
+        session=session,
+        run=False,
+        dirpath=tmp_path,
+        layer_stack=layer_stack,
+    )
+
+    assert ("layer_1_0", "sidewall angle", 80) in session.layer_settings
diff --git a/gplugins/lumerical/write_sparameters_lumerical.py b/gplugins/lumerical/write_sparameters_lumerical.py
index 17b1cfce..0ccf6ae0 100644
--- a/gplugins/lumerical/write_sparameters_lumerical.py
+++ b/gplugins/lumerical/write_sparameters_lumerical.py
@@ -459,6 +459,8 @@ def write_sparameters_lumerical(
 
     exclude_layers = exclude_layers or []
     polygons_per_layer = component_extended_beyond_pml.get_polygons_points(merge=True)
+    layer_builder_name = "gplugins_layer_builder"
+    has_layer_builder = False
 
     for level in layer_stack.layers.values():
         layer = level.layer
@@ -501,11 +503,33 @@ def write_sparameters_lumerical(
             zmax = zmin + thickness
             z = (zmax + zmin) / 2
 
-            s.gdsimport(str(gdspath), "top", f"{layer_tuple[0]}:{layer_tuple[1]}")
-            layername = f"GDS_LAYER_{layer_tuple[0]}:{layer_tuple[1]}"
-            s.setnamed(layername, "z", z * 1e-6)
-            s.setnamed(layername, "z span", thickness * 1e-6)
-            set_material(session=s, structure=layername, material=material)
+            if level.sidewall_angle:
+                if not has_layer_builder:
+                    s.addlayerbuilder()
+                    s.set("name", layer_builder_name)
+                    s.loadgdsfile(str(gdspath))
+                    has_layer_builder = True
+
+                layername = f"layer_{layer_tuple[0]}_{layer_tuple[1]}"
+                s.addlayer(layername)
+                s.setlayer(
+                    layername, "layer number", f"{layer_tuple[0]}:{layer_tuple[1]}"
+                )
+                s.setlayer(layername, "start position", zmin * 1e-6)
+                s.setlayer(layername, "thickness", thickness * 1e-6)
+                s.setlayer(layername, "sidewall angle", 90 - level.sidewall_angle)
+                if not isinstance(material, str):
+                    raise ValueError(
+                        "Layer Builder sidewall angles require a material database name. "
+                        f"Got {material!r} for layer {layer_tuple}."
+                    )
+                s.setlayer(layername, "pattern material", material)
+            else:
+                s.gdsimport(str(gdspath), "top", f"{layer_tuple[0]}:{layer_tuple[1]}")
+                layername = f"GDS_LAYER_{layer_tuple[0]}:{layer_tuple[1]}"
+                s.setnamed(layername, "z", z * 1e-6)
+                s.setnamed(layername, "z span", thickness * 1e-6)
+                set_material(session=s, structure=layername, material=material)
             logger.info(
                 f"adding {layer_tuple}, thickness = {thickness} um, zmin = {zmin} um "
             )