A dummy fin described herein includes a low dielectric constant (low-k or LK) material outer shell. A leakage path that would otherwise occur due to a void being formed in the low-k material outer shell is filled with a high dielectric constant (high-k or HK) material inner core. This increases the effectiveness of the dummy fin to provide electrical isolation and increases device performance of a semiconductor device in which the dummy fin is included. Moreover, the dummy fin described herein may not suffer from bending issues experienced in other types of dummy fins, which may otherwise cause high-k induced alternating current (AC) performance degradation. The processes for forming the dummy fins described herein are compatible with other fin field effect transistor (finFET) formation processes and are be easily integrated to minimize and/or prevent polishing issues, etch back issues, and/or other types of semiconductor processing issues.