To prevent short defects between source/drains of transistors of a complementary cell circuit, isolation walls are formed in an isolation region between the source/drains of the transistors prior to growing a P-type epitaxial layer and an N-type epitaxial layer on respective sides of the isolation region. The isolation walls provide a physical barrier to prevent formation of short defects that can otherwise form between the P-type and N-type epitaxial layers. Thus, the isolation walls prevent circuit failures resulting from electrical shorts between source/drain regions of transistors in complementary cell circuits. A width of the isolation region between a P-type transistor and an N-type transistor in a circuit cell layout can be reduced so that a total layout area of the complementary cell circuit can be reduced without reducing product yield. A gate cut may be formed in the dummy gate with a process of forming the isolation walls.