Methods of in situ fabrication and formation of horizontal nanowires for a semiconductor device employ non-catalytic selective area epitaxial growth to selectively grow a semiconductor material in a selective area opening of predefined asymmetrical geometry. The selective area opening is defined in a dielectric layer to expose a semiconductor layer underlying the dielectric layer. The non-catalytic selective area epitaxial growth is performed at a growth temperature sufficient to also in situ form a linear stress crack of nanoscale width that is nucleated from a location in a vicinity of the selective area opening and that propagates in a uniform direction along a crystal plane of the semiconductor layer in both the semiconductor layer and the dielectric layer as a linear nanogap template. The semiconductor material is further selectively grown to fill the linear nanogap template to in situ form the nanowire that is uniformly linear.