Resistive RAM is a very promising candidate for high density non-volatile memory. Although bipolar operation has been shown to work at lower current (essential for low power, mobile computing) [1], a suitable selector device that delivers high current density and high on/off current ratio is challenging [2–4]. We demonstrate a 4F2 bipolar selector device based on the punch-through mechanism. An npn vertical junction device fabricated using in-situ doped epitaxial silicon is presented. Superior on-current density (Jon=1MA/cm2) and high on-off current ratio (Ion/Ioff) of 300–5000 is experimentally demonstrated. TCAD simulations based performance, variability and scalability are presented.