Gillis released two albums with Rubicon and 14 with Night Ranger. He filled in on guitar for Ozzy Osbourne when Randy Rhoads passed away and played on one album. Gillis released the solo studio albums Gilrock Ranch in 1993 and Alligator in 2000. He has also released albums with Hear ’n Aid, Fiona, Derek Sherinian, Vicious Rumors, and Queensryche with Geoff Tate.