Dark yellow semen may be caused by semen concentration, prostatitis, seminal vesiculitis and other factors. 1. Concentration of semen: Men who do not have sex for a long time and do not have ejaculation may cause too much semen in the seminal vesicles, causing concentration of semen, which will make the semen become dark yellow, without other clinical symptoms. 2. Prostatitis: Sitting for a long time, holding urine for a long time, unclean sex and other factors may induce prostatitis, so that there are inflammatory substances in the prostate fluid, which will make the semen dark yellow, accompanied by perineal distension and pain, urinary frequency, urinary urgency and other symptoms. 3. Spermatitis: it may be related to the infection of neighboring organs, such as prostatitis or urethritis, due to the existence of infection in the seminal vesicles, so that the presence of inflammatory substances in the semen, which can lead to the color of the semen becomes dark yellow, and in severe cases, the local breakage of bleeding, so that the color of the semen becomes red, and accompanied by ejaculatory pain and other symptoms. The dark yellow color of semen should be alerted to disease factors, and medical examination and treatment are recommended.