In this paper, a highly sensitive linear high-temperature sensor based on a 4H-SiC p-i-n diode is introduced. The sensor offers both a very high sensitivity up to 4.5 mV/°C and a high linearity (coefficient of determination R2 up to 99.96%) for temperatures varying from room temperature up to 460 °C. Both parameters, linearity and sensitivity, are current density dependent. The best tradeoff between linearity (R2 of 99.96%) and sensitivity (4.3 mV/°C) was found for an applied current density of 0.7 μA/cm2. The proposed type of sensor is suitable for being integrated, e.g., into a smart high-voltage switch. Furthermore, the current transport mechanisms from room up to higher temperatures deduced from the I-V characteristics are discussed, leading to the conclusion that recombination currents are predominant for a wide range of applied current densities. Thus, the increase in the intrinsic carrier concentration dominates the temperature dependence of the saturation current density. If required, applications at even higher temperatures are possible from the semiconductor point of view. But in this case, further optimizations of the manufacturing process for usability for this temperature range are recommended and discussed.