The forbidden gap in germanium crystal is:

Semiconductors are similar to insulators but the conduction and valence bands are spaced closely, so that at room temperature a number of electrons are found in conduction band.

$$\begin{gathered} \text{ For germanium, forbidden energy gap }=0.7 \mathrm{eV} \\ = 0.7 \times 1.6 \times {10}^{-19} \mathrm{J} = 1.12 \times {10}^{-19} \mathrm{J} \end{gathered}$$