Properties of deep levels in vapor-deposited ZnSe on GaAs have been investigated using transient photocurrent and steady state photocapacitance measurements. A metal/insulator/semiconductor structure was used in the study in which ZnSe formed the insulator. A single dominant deep level in the ZnSe having an energy of E c − 1.2 eV was observed over the spectral region 0.5–3.0 eV. The photoionization cross section of the trap at 1.5 eV and 295 K is 7 x 10 16 cm 2. Trap concentrations in the range 10 16−10 17 cm −3 were measured in the as-grown material.