In this article it is presented the impact of the one-port substrate characterization technique on the implementation of a RF power amplifier. We used single port measurements as difference with conventional methods, which use two port measurements. It demonstrates to be a practical way to measure the permittivity and losses of substrates with high accuracy. One of the advantages of the proposed method is its simplicity and the fact that the use of Vector Network Analyzers is not required. This method can be used as a low cost solution for substrate characterization. A 3.5 GHz high power amplifier in LDMOS technology was designed and implemented with this technique validating the method of substrate characterization at this high frequency and at high power levels. Thermal measurements were carried out for the first time in order to demonstrate that the circuit does not exceed the limits for this kind of substrate. From electrical point of view it was demonstrated that the gain variation with respect to the temperature is within the normal limits for LDMOS.