The present paper reports a 2.8-mm-square surface-mountable MEMS-on-LSI integrated 3-axis tactile sensor for robot applications, which incorporates sensing and signal processing in a single chip. The MEMS part has a quad-seesaw-electrode structure for fully-differential capacitive 3-axis force sensing. The LSI is an original sensor platform LSI equipped with deep annular-type through silicon vias (TSVs). A multi-project LSI wafer was processed after fabrication in an LSI foundry. The MEMS part and the LSI part were integrated by Au-Au thermocompression bonding. The output is a digital packet and is transferred through the TSV and a bus line. A working test successfully demonstrated the fully-differential capacitive 3-axis force sensing of the fully-integrated tactile sensor.