The delay time of forward current onset from initial electron space‐charge‐limited current to recombination‐limited current in a‐Si:H p‐i‐n devices was studied as a function of bias voltage, temperature and illumination intensity. The results show that the delay time and the initial electron current are related by a power law, td∝I−γSCLC, where γ is a temperature‐independent constant. The value of γ is sensitive to the device properties such as the thickness of the intrinsic layer and the density of states. For a good quality device with 3.74 μm intrinsic layer, γ=0.70±0.05, while for a thin one deposited in the same conditions, γ changes to 0.99±0.05. A physical interpretation is presented. © 1994 American Institute of Physics.