Achieving　economic　orientation-controlled　growth　of　monolithic　nanowires　remains　a　challenge.　We　report　a　simple　and　low-cost,　endotaxial,　self-templating,　noncatalyzed　synthesis　of　monolithic　boron　nitride　semiconductor　nanowires.　The　method　uses　orientated　control　of　the　nanowires　prepared　directly　on　Si　substrates　through　plasma-enhanced　chemical　vapor　deposition　without　a　catalyst.　The　growth　direction　of　the　synthetic　monolithic　nanowires　is　controlled　as　a　function　of　substrate　crystal　orientation.　We　measured　the　vertical　electrical　properties　of　the　nanowires.　Our　method　provides　an　alternative　strategy　to　control　monolithic　nanowire　growth　in　substrates,　and　may　allow　for　large-scale,　low-cost　nanowire　device　manufacture.