In this paper, we demonstrate the feasibility of selective extracellular electrical stimulation at the (sub)cellular level in dissociated cultured cells. Using a CMOS-compatible process, we have fabricated an electrode array with sub-micrometer nail probes. Due to their particular configuration, the nails are strongly engulfed by the cellular membrane. By measuring the calcium signals, we found that electrical stimulation via the micronails activates the cell locally, in a dose-dependent manner, with very low applied currents. The results suggest the applicability of the device in pharmacological or signal propagation studies.