The present work deals with the electrical and optoelectronic characterizations of the isotype GaAs 15 P 85 /GaP devices prepared by liquid phase epitaxy. The electrical properties of the fabricated junction were studied by analyzing its current-voltage (I-V) characteristics, capacitance-voltage (C-V) characteristics in the dark at different temperatures in the range of 300-450 K. The analysis of dark current-voltage (I-V) characteristics at different temperatures were presented in order to elucidate the conduction mechanism and to evaluate the important device parameters. The predominant charge transport mechanism in these devices was found to be thermionic emission in the depletion layer and over the barrier of GaAs 15 P 85 /GaP heterojunction at forward bias voltage. From the capacitance-voltage, measurements at high frequency (1 MHz) information can be obtained about the carrier concentration, the diffusion potential, the barrier height of GaAs 15 P 85 /GaP heterojunction. The current-voltage characteristics of the GaAs 15 P 85 /GaP heterojunction under different illumination intensities were studied. The power low dependence of the reverse current voltage is characterized by space charge limited conduction, SCLC dominated by exponential trap distribution at the higher reverse voltage region.