This research is about investigating the third-order intercept point (TOI) and nonlinear distortion level (NDL) for two GaN HEMTs of different gate lengths with temperature and frequency. As a multi-biasing, input power, frequency and temperature-dependent term; the TOI point and as well as the nonlinear distortion level are particular figures merit relevant to the third-order intermodulation distortion (IMD3) product. The primary results are the output referenced TOI reduced whereas the input referenced TOI raised as the frequency goes higher and the lower gated device exhibits a bit greater magnitude. Over the temperature range measured; the magnitude of TOI and nonlinear distortion considerably changed in accordance to the performance of third order intermodulation distortion (IMD3) component. This investigation of TOI is used to determine what extent distortion is generated, and comparing that to the entryway of the antenna provides a clear strategy for determining if the spec can be met or not. However, distortion level investigation is a critical point to choose the best biasing preference with the device's inlet measurements to establish a solution that fits with the intended usage.