Heterojunction diodes fabricated by thermal evaporation of p-type amorphous selenium (a-Se) on various crystalline wafers (n-Si, p-Si and n-GaAs) are analyzed by measuring their current-voltage (J-V) characteristics. The measured J-V characteristics for the investigated devices of configuration Au/a-Se/c-wafer/Al, exhibit a rectifying behavior and the bulk effect of the a-Se layer. For low forward voltage, the conduction mechanism is dominated by recombination of the carriers in the amorphous side of the space charge region. At higher voltage, the J-V characteristics could be divided into two regions: an ohmic region and a space charge limited current region. The values of the activation energy obtained from the ohmic region are in agreement with those obtained from dc conductivity measurements in the same range of temperature. The reverse bias activation energy values at different temperatures are in agreement with those obtained from the temperature dependence of the forward saturation current, supporting the proposed recombination mechanism of conduction. (C) 2009 Elsevier B.V. All rights reserved.