We have studied the photovoltage decay curve of porous silicon(PS)for the first time.The photovoltage decay curve is quiet different from that of single crystalline Si

the maximum of photovoltage is stronger than that of Si.The photovoltage decay curve of PS indicates that the photovoltage quickly appears after laser pulses

and then changes slowly with many small unstable peaks until a photovoltage pulse appears

the photo-voltage begins to decrease slowly only after the photovoltage pulse appears.This phenomenon is attributed to charge storage on PS surface and the charge exchanging between the interface states and crystalline Si substrate.