Bipolar transistor structure and radio frequency amplifier

A semiconductor device, comprising:

• an active region, wherein the active region comprises:
• a semiconductor layer, having a first surface, wherein the semiconductor layer comprises a collector layer, a base layer and an emitter layer sequentially stacked in that order;
• and the first surface is a surface of the emitter layer facing away from the base layer;
• an emitter mesa, disposed on the emitter layer;
• an emitter electrode, disposed on the emitter mesa;
• a first dielectric layer, covering a top surface of the emitter electrode, and extending along a side surface of the emitter electrode to cover a part of the first surface exposed outside the emitter electrode;
• wherein the first dielectric layer defines a first opening;
• a second dielectric layer, covering the first dielectric layer;
• wherein the second dielectric layer defines a second opening connected to the first opening;
• and
• a base electrode, connected to the base layer through the first opening and the second opening, and extending laterally to directly cover at least a part of an upper surface of the second dielectric layer adjacent to the second opening;
• and
• wherein a thickness of each of the first dielectric layer and the second dielectric layer is in a range of 200 angstroms (Å) to 1000 Å;
• a maximum width of the first opening is in a range of 0.2 microns (μm) to 1 μm, and a maximum width of the second opening is in a range of 0.2 μm to 1 μm;
• and a minimum distance between the first opening and the emitter mesa is in a range of 0.2 μm to 1 μm.