To obtain the half-degummed silk yarns of 5~10% degumming losses, raw silk yarns were degummed with alkaline detergent after fixing sericin with formaldehyde. Adding above 5 g/l acetic acid or tartaric acid in 1% and 5% formaldehyde fixing baths created a lot of sericin loss during degumming with 3 g/l alkaline detergent and 2 g/l sodium carbonate after fixing sericin due to alkaline hydrolysis of sericin cross-linkage. When sericin was degummed with 3 g/l alkaline detergent after fixing with 0.1% formaldehyde at $40^{circ}C$ or $60^{circ}C$ for 15 min, the degumming temperature necessary to obtain satisfactory half-degumming was $70{sim}80^{circ}C$. Also, fixing sericin at $60^{circ}C$ resulted in stronger sericin fixation than fixing at $40^{circ}C$. However, the softener of cationic surfactant added in sericin fixing baths did not prevent the attachment of degummed silk yarns. Approximately 6.5% degumming loss was obtained when sericin was degummed at $85^{circ}C$ for 30 min with 3 g/l alkaline detergent after fixing with 0.1% formaldehyde at $80^{circ}C$ for 15 min and 30 min, and in case of adding 2 g/l acetic acid in fixing baths the half-degummed silk yarns of about 10% degumming losses, which were severely attached to each other, were obtained.