Single crystal ZnIn2S4 layers were grown on thoroughly etched semi-insulating GaAs(100) substrate at 450oC with hot wall epitaxy (HWE) system by evaporating ZnIn2S4 source at 610oC. The crystalline structure of the single crystal thin films was investigated by the photoluminescence (PL) and double crystal X-ray rocking curve (DCRC). The temperature dependence of the energy band gap of the ZnIn2S4 obtained from the absorption spectra was well described by the Varshni’s relation, Eg(T) = 2.9514 eV-(7.24 × 10.4 eV/K)T2/(T＋ 489 K). After the as-grown ZnIn2S4 single crystal thin films were annealed in Zn-, S-, and In-atmospheres, the origin of point defects of ZnIn2S4 single crystal thin films has been investigated by the photoluminescence (PL) at 10 K. The native defects of VZn, VS, Znint, and Sint obtained by PL measurements were classified as a donors or acceptors type. And we concluded that the heat-treatment in the S-atmosphere converted ZnIn2S4 single crystal thin films to an optical p-type. Also, we confirmed that In in ZnIn2S4/GaAs did not form the native defects because In in ZnIn2S4 single crystal thin films existed in the form of stable bonds.