diff --git a/mkdocs.yml b/mkdocs.yml
index 5b29a689e342f3cad21d8b9f77f900c366d99b6e..5f1888964824c70bb26ef3dcb0de27d787cb7e98 100644
--- a/mkdocs.yml
+++ b/mkdocs.yml
@@ -47,7 +47,7 @@ nav:
     - X-ray diffraction: '10_xray_solutions.md'
     - Nearly free electron model: '11_nearly_free_electron_model_solutions.md'
     - Band structures in 2D: '12_band_structures_in_higher_dimensions_solutions.md'
-    # - Basic principles: '13_semiconductors_solutions.md'
+    - Basic principles: '13_semiconductors_solutions.md'
     # - Doping and devices: '14_doping_and_devices_solutions.md'
 
 theme: