Results are reported from an experimental study of the effects of the external and internal resonator parameters on the spectral and spatial characteristics of emissions from electron-beam pumped semiconductor laser (EBPL). The EBPLs examined had either an internal resonator, an external resonator, or both. CdS semiconductors fitted with a reflective Ag coating on one side and a sapphire plate on the other were exposed to a 30 kV, 0.2-3 mA electron beam with a pulse length of 10 nsec and a repetition rate of 0.5-20 kHz. Measurements made of the lasing pulse shape, peak power and spectra showed that laser power and efficiency were higher and the threshold values lower in the EBPL without an external cavity than in devices with external cavities. Prominent off-axis modes were also observed with external cavities at frequencies which satisfied refraction and dispersion characteristics of both internal and external resonators.