We report here a simple alternative method for measuring charge carrier drift mobilities in semiconductor devices. A typical falling photocurrent transient formula for switch-off-state was adjusted to obtain simultaneously electron and hole mobilities. For both undoped ZnO film and InAlAs/InGaAs quantum well structure, electron mobilities extracted from our model were compared with those obtained from maximum-entropy mobility-spectrum analysis method (ME-MSA). Our results demonstrated that electron mobility obtained from our photocurrent response model could serve as substitutes for a representative mobility obtained from ME-MSA.