BASIC ELECTRONICS is the second of three books prepared by engineer Albeiro Patiño Builes. The analysis now focuses on semiconductors, the primary basis of digital electronics. It analyzes diodes and circuits with diodes, as well as the bipolar junction transistor (BJT), and the application of these components to practical and real cases. The author dedicates a following chapter to the study of various devices used in digital circuits, such as batteries, switches, pushbuttons, fuses, varistors, resistors, potentiometers, capacitors, coils, light-emitting diodes, photovoltaic cells, integrated circuits, speakers, and more. He continues with a practical case that will be very interesting for students, and is the step-by-step analysis that will lead readers of this text to the design and construction of a power supply, which will be of great help in providing direct current energy from alternating current energy for their next works. Finally, there is an academic support guide, consisting of a series of proposed practical exercises that will allow the student not only to put their learning into practice, but also to have fun with their creations, such as current rectifiers, voltage multipliers, amplifiers, regulators, light sources, and more.