Can I extend my stay Singapore for another 90 days without traveling other countries?

You can apply online through the Immigration & Checkpoints Authority

Apply to Extend Stay

Visitors who are in Singapore as a tourist for social purposes or seeking medical treatment, and require a longer period of stay beyond the Visit Pass granted on entry into Singapore, may submit an application for extension of stay (not more than 89 days from date of entry) online using the e-Service.

To submit an application online using the e-Service, you will need to fulfil all of the following conditions:

• You wish to extend your stay for not more than 89 days from the date of entry into Singapore
• Your Visit Pass has a remaining validity of at least three days, excluding weekends and public holidays
• You will not return to Singapore within five days from the departure date of your current trip

National of certain countries do require a local sponsor; South Korea is not among those listed.

You will need to have the following ready:

• Your travel document (e.g. passport) with at least 6 months validity. A copy of the travel document’s personal particulars page must be submitted to ICA.
• Your Disembarkation/Embarkation (D/E) card with a valid Visit Pass granted on entry into Singapore
• Original supporting documentary evidence to establish relationship will be required if you are a foreigner with family ties where your immediate family members are Singapore citizens or permanent residents
• A VISA credit card, a MasterCard credit or debit card or a valid Internet Banking account in Singapore with DBS/POSB, OCBC, UOB, Standard Chartered Bank and Citibank, for payment (if applicable)
• Form V75, duly endorsed by a registered doctor in Singapore, stating the details of the illness and the period of stay required if you are seeking extension of stay for medical treatment