Thermal convective accelerometers are based on heat transfer in a fluid-filled cavity. The principle is well known and the first MEMS implementations were reported in the late 90's. Since that time, many single-axis or dual-axis sensors were reported. The device presented in this paper is the first reported 3-axis sensor manufactured in a standard CMOS technology. Therefore, the goal of this study is to demonstrate the feasibility of a third sensitive axis on a single device and to provide MEMS designers with a compact model and the main parameters that govern the sensitivity.