Aspect ratio trapping in channel last process

A method of forming a semiconductor device comprising:

• forming a replacement gate structure on a channel region of the at least one replacement fin structure;
• forming an encapsulating dielectric that encapsulates the replacement fin structure leaving a portion of the replacement gate structure exposed;
• etching the portion of the replacement gate structure that is exposed to provide an opening through the encapsulating dielectric to the replacement fin structure;
• etching the replacement fin structure selectively to the encapsulating dielectric to provide a fin opening;
• functional fin structures of a second semiconductor material are epitaxially grown on a growth surface of the substrate exposed by the fin opening;
• and
• replacing a remaining portion of the replacement gate structure with a functional gate structure.

A semiconductor device comprising:

• a substrate of a type IV semiconductor material having a trench present therein;
• a plurality of type III-V fin structures joined by an epitaxial base portion that is present within the trench of the type IV semiconductor material, wherein the epitaxial base portion in epitaxial relationship with the trench of the type IV semiconductor substrate;
• a gate structure present on a channel region portion of the type III-V fin structures;
• and
• source and drain regions present on source and drain region portions of the type III-V fin structures.