  We discuss a phase transition of a Reissner-Nordstr\"om black hole to a hairy
black hole in asymptotically flat spacetime. The hair is due to a massive
charged scalar field. The no-hair theorem is evaded thanks to a derivative
coupling of the scalar field to the Einstein tensor. The resulting hairy
configuration is spherically symmetric. We solve the equations analytically
near the transition temperature and show that the hair is concentrated near the
horizon decaying exponentially away from it.
