Catalyst-free,　selective　growth　of　ZnO　nanowires　directly　on　the　commonly　used　dielectric　SiO2　layer　is　of　both　scientific　significance　and　application　importance,　yet　it　is　still　a　challenge.　Here,　we　report　a　facile　method　to　grow　single-crystal　ZnO　nanowires　on　a　large　scale　directly　on　SiO2/Si　substrate　through　vapor　solid　mechanism　without　using　any　predeposited　metal　catalyst　or　seed　layer.　We　found　that　a　rough　SiO2/Si　substrate　surface　created　by　the　reactive　ion　etching　is　critical　for　ZnO　growth　without　using　catalyst.　ZnO　nanowire　array　exclusively　grows　in　area　etched　by　the　reactive　ion　etching　method.　The　advantages　of　this　method　include　facile　and　safe　roughness-assisted　catalyst-free　growth　of　ZnO　nanowires　on　SiO2/Si　substrate　and　the　subsequent　transfer-free　fabrication　of　electronic　or　optoelectronic　devices.　The　ZnO　nanowire　UV　photodetector　fabricated　by　a　transfer-free　process　presented　high　performance　in　responsivity,　quantum　efficiency　and　response　speed,　even　without　any　post-treatments.　The　strategy　shown　here　would　greatly　reduce　the　complexity　in　nanodevice　fabrication　and　give　an　impetus　to　the　application　of　ZnO　nanowires　in　nanoelectronics　and　optoelectronics.