Pressure-induced phase switching of Shubnikov–de Haas oscillations in the molecular Dirac fermion system <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:mi>?</mml:mi><mml:mtext>?</mml:mtext><mml:msub><mml:mrow><mml:mo>(</mml:mo><mml:mi>BETS</mml:mi><mml:mo>)</mml:mo></mml:mrow><mml:mn>2</mml:mn></mml:msub><mml:msub><mml:mi mathvariant="normal">I</mml:mi><mml:mn>3</mml:mn></mml:msub></mml:mrow></mml:math>

We report on the Shubnikov de Haas (SdH) oscillations in quasi two-dimensional molecular conductor $\alpha-$(BETS)$_{2}$I$_{3}$ [BETS: bis(ethylenedithio)tetraselenafulvalene] laminated polyimide films at 1.7 K. From SdH phase factor, we verified experimentally that material is Dirac fermion under pressure. vicinity of transition between strongly correlated insulating and phases, a possible candidate for an ambient-pressure system. However, indicate Berry zero ambient Under pressure, $\pi$ emerges when metal-insulator crossover almost suppressed $\sim$0.5 GPa. The results contrast those pioneering system $\alpha-$(BEDT-TTF)$_{2}$I$_{3}$ [BEDT-TTF: bis(ethylenedithio)tetrathiafulvalene] which fermions semiconducting behavior are simultaneously observed.