Monolithic mass sensors for ultrasensitive mass detection in air conditions have been fabricated using a conventional 0.35 μm complementary metal-oxide-semiconductor (CMOS) process. The mass sensors are based on electrostatically excited submicrometer scale cantilevers integrated with CMOS electronics. The devices have been calibrated obtaining an experimental sensitivity of 6× 10-11 g cm2 Hz equivalent to 0.9 agHz for locally deposited mass. Results from time-resolved mass measurements are also presented. An evaluation of the mass resolution have been performed obtaining a value of 2.4× 10-17 g in air conditions, resulting in an improvement of these devices from previous works in terms of sensitivity, resolution, and fabrication process complexity.