A micro-Pirani vacuum sensor with an operating pressure range of more than 5 decades is described. The device is fabricated by applying a low-resolution and potentially low-cost front-side bulk micromachining step to a chip produced with a commercial CMOS technology. Maximization of the thermally coupled surfaces has been obtained by stacking all layers available by default in the CMOS process. This design choice and the integration of a low-noise, low-power readout interface allowed achievement of state-of-art performances with a fabrication approach affordable even to SMEs and small University laboratories.