Recently, portable electronic equipment driven by batteries has been developed one after another in various fields such as mobile communication, healthcare, and so on. Accordingly, demands for value-added products integrated with various sensors are growing in these fields. A pressure sensor for measuring atmospheric pressure is one of the devices that attract attention. In addition, the miniaturization and the low power consumption of the sensor are indispensable to the portable electronics. To meet the demand, we have developed a new digital output ultrasmall atmospheric pressure sensor that works with low power consumption. In this report, the features of the developed sensor are described. Portable electronic equipment has achieved a remarkable development. As typified by smartphones and tablet PCs, a number of small and lightweight equipment has been developed and widely used by consumers. Electronic devices employed in such portable equipment are required to be small and light. In addition, they have to work with low power consumption for saving battery life. Among the electronic devices, sensors based on Micro Electro Mechanical Systems (MEMS) technology, such as an accelerometer or a gyroscope, have been attracting much attention since they bring new functions to such portable equipment. Recently, an atmospheric pressure sensor has been becoming an option to introduce new functions to those devices. The most common atmospheric pressure sensors use piezo-resistive effect and are manufactured by silicon planer processes and MEMS technology. The sensor described in this paper is also a piezo-resistive-type sensor. The pressure sensor outputs DC voltage proportional to the applied pressure by using a Wheatstone bridge circuit that includes four piezo-resistive resistors. Although the output voltage accurately reflects the ambient pressure, the amount of voltage change of the sensor element itself is very small, and the output voltage also varies with ambient temperature changes due to an inherent nature of a semiconductor. Therefore, amplifying and compensating functions by an integrated circuit are required in practical use. To meet such requirements, two types of sensors have already been developed and used as commercial products. One is a “One-chip integrated pressure sensor” 1) into which a sensor element