diff --git a/docs/13_semiconductors.md b/docs/13_semiconductors.md
index 0f5bcf868d85d757924a52136603399dbd2021ba..6a1ee6f7c951fe5bd3f15c90e1456bf723290015 100644
--- a/docs/13_semiconductors.md
+++ b/docs/13_semiconductors.md
@@ -57,7 +57,7 @@ Before proceeding further, let us remind ourselves of important band structure p
 Descibes how quickly electrons move within the lattice. 
 * Effective mass $m^* = \hbar^2\left(d^2 E(k)/dk^2\right)^{-1}$. 
 Tells us how hard it is to *accelerate* the particles and is related to the curvature of the band.
-* Density of states $g(E) = \sum_{\textrm{FS}} (dn/dk) \times (dk/dE)$. 
+* Density of states $g(E) = \sum (dn/dk) \times (dk/dE)$, where the sum runs over all states at the same energy. 
 The amount of states per infinitesimal interval of energy at given energy. 
 The quantity is vital in order to calculate any bulk property of the material such as conductivity, heat capacity, etc.