III-nitrides InGaN solar cells have exhibited many favorable physical properties for space photovoltaic (PV) applications. Here we demonstrate the first nonpolar and semipolar InGaN/GaN multiple-quantum-well (MQW) solar cells grown on nonpolar m-plane and semipolar (2021) plane bulk GaN substrates. The optical properties and PV performance of these InGaN solar cells were systematically studied, including the absorption spectra, current density-voltage (J-V) characteristics, external quantum efficiency (EQE), and internal quantum efficiency (IQE). Overall nonpolar m-plane InGaN/GaN MQW solar cells demonstrated the best performance across all devices, with a high open-circuit voltage and the highest EQE and IQE. This huge difference is attributed to the better carrier transport and collection on nonpolar m-plane devices due to the reduced polarization effects, which were further confirmed by bias-dependent EQE measurements. Furthermore, high temperature measurements reveal that peak EQE values exceeds 80% at 500 °C and a positive thermal power coefficient up to 350 °C for nonpolar m-plane solar cells. These results demonstrate the high potential of nonpolar and semipolar InGaN solar cells for high temperature PV applications, which are required for space missions close to the sun.