In this article, a new functional resonant tunneling base transistor (RTBT) with an AlGaAs/GaAs/InGaAs heterostructure emitter and an ultra-thin base layer was fabricated and demonstrated. The bi-directional negative-differential-resistance (NDR), i.e., N- and S-shaped NDR, are observed under the normal and inverted operation mode, respectively. In this device, typical transistor performances with common-emitter current gain of 140 and a low offset voltage of 100 mV, incorporating an interesting N-shaped NDR phenomenon with peak-to-valley current ratio of 5.3, are attained at room temperature. The behavior is mainly attributed from electrons resonant tunneling from depleted GaAs emitter to collector barriers, through InGaAs quantum well (QW) and ultra-thin base layer. On the contrary, the multiple S-shaped NDR behaviors resulting from an avalanche multiplication and successive two-stage barrier lowing process under inverted operation mode are observed.