Foreigners who stay or work in Singapore for at least 183 days in a calendar year are generally treated as Singapore tax residents. Other residency rules may also apply, including the 3-year rule and certain employment periods spanning 2 calendar years.
IRAS — Working out my tax residency: https://www.iras.gov.sg/taxes/individual-income-tax/basics-of-individual-income-tax/tax-residency-and-tax-rates/working-out-my-tax-residency