Embodiments herein describe dummy gates disposed over a portion of a fin in finFETs. That is, instead of separating the dummy gates from the finFET structure, the fins may be extended and covered, at least partially, by the dummy gates. An insulative material is disposed between the dummy gate and the fin in order to form a decoupling capacitor. In one embodiment, the dummy gate overlaps a portion of the fin that is held at a voltage rail. Moreover, the dummy gate may be coupled to a different (e.g., opposite) voltage rail than rail coupled to the fin. For example, if the fin is coupled to VHIGH then the dummy gate is coupled to VLOW, or vice versa. Thus, the capacitor formed using the fin and the dummy gate provides a decoupling capacitance between the power sources generating the voltage rails (i.e., VHIGH and VLOW).