Sergio Osmeña is a mountainous municipality in the southern part of Zamboanga del Norte, Region IX. It is 48 kilometres from Dipolog City – center of trade of the province, and 90 kilometres from Dapitan City of Zamboanga del Sur. It is traversed by a national road connecting Zamboanga del Norte and Zamboanga del Sur. It has a total land area of 55,644 hectares. The municipality is rectangular in shape and is bounded by the municipalities of Katipunan, Piñan, Mutia, Josefina, and Dumingag.
According to Philippine Statistics Authority, it became a municipality by virtue of Republic Act No. 3697 also known as “An Act of Creating the Municipality of Sergio Osmeña” on September 14, 1963.
Sinai is one of the 39 barangays of Sergio Osmeña, a second-class municipality (partially urban). It is bounded by barangay Situbo in the north-west, Poblacion Alto and Poblacion Bajo in the west, Buenavista in the east, Venus and Tinindugan in the south. It is a small proportion of the municipality with a total area of 327 hectares.
The barangay is situated at the foot of a mountain and its first inhabitants were said to be religious people. They then derived its name from the story of Moses at Mt. Sinai of the bible. It was created on January 5, 1972.