In this paper, a CMOS temperature sensor is proposed to measure the internal temperature of a chip. The temperature sensor consists of a proportional-to-absolute-temperature (PTAT) circuit for a temperature sensing part and a 4-bit analog-to-digital converter (ADC) for a digital interface. The PTAT circuit with the compact area is designed by using a vertical PNP architecture in the CMOS process. To reduce sensitivity of temperature variation in the digital interface circuit of the proposed temperature sensor, a 4-bit successive approximation (SA) ADC using the minimum analog circuits is used. It uses a capacitor-based digital-to-analog converter and a time-domain comparator to minimize power consumption. The proposed temperature sensor was fabricated by using a $0.25{mu}m$ 1-poly 6-metal CMOS process with a 2.5V supply, and its operating temperature range is from 50 to $150^{circ}C$. The area and power consumption of the fabricated temperature sensor are $130{ imes}390{mu}m^2$ and $868{mu}W$, respectively.