Errors caused by tolerance variations and mismatches among components severely degrade the performance of integrated circuits. These random effects in process parameters significantly impact manufacture costs by decreasing yield and so by including extra-circuits for adjustment. In this paper we propose a design methodology based on the Pelgrom's MOS transistor-mismatching model devices. Our main objective is to calculate the size of each component considering their relation between area and mismatching. Therefore, in order to validate our proposal methodology, we used as a design target a bandgap reference circuit fabricated in 0.35\mum CMOS technology. Its temperature coefficient attains an average value of 40ppm/oC and an average output voltage of 1,20714V. It also includes a straightforward 4-bits trim circuit to achieve more process independence variation. As a result of our methodology, the considerable area of 400x350\mum^2 was occupied due to our matching design requirements.