This paper presents a compact temperature sensor that directly controls a temperature-dependent self-refresh period of a mobile DRAM in 28nm CMOS. It uses a dynamic threshold MOST (DTMOST) as a sensing device that periodically discharges a capacitor. The discharging voltage across the capacitor denotes a supply-independent behavior and the temperature-dependent discharging period of the DTMOST diode is detected by incorporating it into a relaxation oscillator. The sensor occupies only 0.017mm2 and achieves a 3σ inaccuracy of ±0.9°C from -10 to 90°C after 1-point trim. Operating from 0.85 to 1.15V, it shows a low supply sensitivity of 0.27°C/V at room temperature. It consumes 33.75μW and achieves a resolution of 10.2mK. This corresponds to a resolution FoM of 0.36pJ· K2.