In the article we report on results of epitaxial growth of GaN on Si substrate in the new HVPE reactor. The reactor was designed for growth of GaN on substrates with diameter up to 76 mm. Thin layer of AlN were deposited in MOCVD reactor in order to prevent reaction between Ga and Si. 10-micron-thickness flat GaN layers were fabricated on MOCVD AlN/Si by HVPE. The GaN layers were characterized by PL, XRD, SEM and mercury probe. The FWHM of XRD rocking curves for GaN peak (0002) was about 500 arcsec, that is similar for the best samples MOCVD GaN/Si.