Bismuth telluride based alloys are electronic semiconductors, which exhibit n- or p-type conduction due to the formation of Te vacancies or antisite defects, i.e., substitution of Bi on Te site or vice versa. Here, it is demonstrated that the temperature dependent Seebeck coefficient of Bi₂Te_2.7Se_0.3 exhibits a reversible change in conduction from p- to n-type at temperatures >487 K without exhibiting any structural transformation. The detailed characterization revealed that conversion of Bi_Te/Se antisite defects into Te vacancies is responsible for the p–n transition. The observed p–n transition makes Bi₂Te_2.7Se_0.3 an ideal candidate for temperature controlled electronic switches.