As a fundamental study to develop ohmic contact material and process, Ge/Ni/ZnSe interfacial reaction and electrical property would be investigated. After annelaing at $170^{circ}C$ for 10min, NiGe was the first phase in the Ge/Ni interface and fine $Ni_3Se_2$ phase was observed at the Ni/ZnSe interface. As Ni reacted with Ge, Ni was deficient in Ge/Ni interface and no more interfacial reaction could occurred. In order to evaluate Schottky barrier height of Ge/Ni/p-ZnSe diode, C-V measurements were carried out for Ge/Ni diodes before and after annealing at temperature ranged form $130^{circ}C$ to $410^{circ}C$ for 10 minute under $N_2$ atmosphere. The Schottky barrier height was 1.3eV at as-deposited state and it decreased rapidly to 0.44eV after annealing at $170^{circ}C$. Considering interfacial reaction, we can conculde that the reaction phase at Ni/ZnSe interface lowered Schottky barrier height.