This paper presents a time-based method of measuring temperature using CMOS thyristors and a time-to-digital converter (TDC) akin to algorithmic analog-to-digital converters. By treating time as a signal and as an abundant resource for slow-changing quantities like temperature, slow but energy-efficient topologies like CMOS thyristors could prove useful. Coupled with a TDC that does not scale exponentially with resolution, a significantly lower energy consumption is achieved. This sensor system measures temperature with non-linearity error of ±0.25 °C and resolution of 0.05 °C per LSB from -15 °C to 30 °C while using only 0.4nJ per measurement.