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In this paper, we report very abrupt current switching and hysteresis effects due to saddle point and impact ionization in low doped n-channel Omega-Gate MOSFET (Omega-MOSFET). The Omega-MOSFETs are fabricated on low-doped (8x10(14)cm(-3)) bulk silicon by bulk silicon isotropic etching and sacrificial oxidation. A specific abrupt impact ionization and hysteresis of I-D(V-DS) are observed at high drain voltage (V-DS > 11V) on transistors that have short channel effects (L=0.9-10um). This is explained by the accumulation of a hole pocket under the gate due to the formation of a saddle point region. An outstanding feature is that this effect can be exploited to abruptly switch from low to high current (2 decades of current) states of I-D(V-GS) characteristics with ultra-abrupt slopes of 5 to 10mV/dec. Moreover, the hysteresis window Delta V-GS similar to 500mV is suitable for DRAM memory. Dynamic switching characteristics and a retention time of up to tens of seconds are originally demonstrated. The proposed Omega-MOSFET stands as a very promising alternative to I-MOS devices, being more scalable and integrable on a standard (low cost) bulk-Si Multi-Gate FET platform. Its experimental performances are promising for both small-slope switches and dynamic RAM memories.