Positron lifetime experiments show the formation of voids in deformed n-type GaAs. In addition, the concentration of monovacancies is increased from the native population by a factor of three to six, depending on the deformation and annealing conditions of the material. The strong temperature dependency of the positron lifetime spectrum also indicates that the concentration of negative ions in deformed GaAs is increased compared to the as-grown material. The authors attribute this to the formation of Ga antisite defects during deformation.