Secondary emission measurements have been made on thick and thin epitaxially grownp‐doped GaAs. Reflection mode gains of 400 at primary voltages of 20 kV have been observed for unthinned layers. The variation of gain with white‐light photoresponse has also been measured. For 5‐&mgr;‐thick self‐supporting layers, a gain of 115 and 30 (at 10 kV primary voltage) has been measured for the reflection and transmission modes, respectively. The escape depth is estimated to be 2 &mgr; with an escape probability of 0.14.