The diallel crossing system is an important tool for selecting parents with a high frequency of favorable alleles and identifying hybrids with high heterosis for traits of interest. This study aimed to evaluate the general and specific combining abilities of yellow melon inbred lines and to estimate heterosis in their hybrid combinations for fruit yield and quality. Seven yellow melon inbred lines (L1-L7) were used to generate 21 single-cross hybrids through a half-diallel mating scheme without reciprocals. Two trials were conducted in different locations in 2024, using a randomized complete block design with three replications and ten plants per plot. The traits analyzed were average fruit weight, yield, flesh thickness, shape index, flesh firmness, and total soluble solids content. Diallel analysis was performed according to Griffing's Method II (Parents and Hybrids), considering a fixed-effects model to estimate general (GCA) and specific (SCA) combining abilities. Heterosis was calculated based on the means of parents and hybrids. Additive and non-additive gene effects control yield, average fruit weight, flesh thickness, and soluble solids content, whereas flesh firmness and shape index are governed exclusively by additive gene effects. Line L1 exhibits a high frequency of favorable alleles for increasing yield, average fruit weight, flesh thickness, and soluble solids content. In contrast, line L4 shows a higher frequency of alleles associated with increased soluble solids content. The hybrid combination between inbred lines L1 and L7 stood out for its high yield and quality performance, along with positive heterosis. Highly significant and positive correlations were found between SCA effects and heterosis, indicating that hybrids with high SCA values tend to exhibit greater heterosis. The results indicate the potential for exploiting heterosis and selecting superior parents for yellow melon breeding programs in semi-arid regions.