Chaz Bono Changes ... His Name

Chaz Bono is taking another major step in his gender transition -- he's applied to legally change his name.

TMZ has learned Chaz filed an application last week at L.A. County Superior Court to change his name from his female birth name Chastity Sun Bono -- to Chaz Bono.

As we first reported, Chaz began the gender transition process in 2009.

Bono Family Fun Fact: Cherilyn Sarkisian Bono Allman legally changed her name to just Cher in 1979.