When forming the strain-inducing semiconductor alloy in one type of transistor of a sophisticated semiconductor device, superior thickness uniformity of a dielectric cap material of the gate electrode structures may be achieved by forming encapsulating spacer elements on each gate electrode structure and providing an additional hard mask material. Consequently, in particular, in sophisticated replacement gate approaches, the dielectric cap material may be efficiently removed in a later manufacturing stage, thereby avoiding any irregularities upon replacing the semiconductor material by an electrode metal.