Al doped ZnO (AZO) films were deposited on porous silicon (PS) substrates by a reactive rf-cosputtering process from two targets of ZnO and Al. The effect of ZnO target rf-sputtering power on the structural and photoluminescence (PL) properties of AZO/PS heterojunctions were studied. Strong monochromatic blue emission located at 2.78 eV was observed for the AZO films deposited at 150 W. Freshly prepared PS showed an emission band in the green spectral region. We show that deposition of AZO on PS does not degrade the skeleton of the PS and enhance the PL intensity. The PL band shifted to the high energy for AZO films deposited on PS and the intensity became stable.