In Jainism, Sidhi Tap (also known as Siddhi Tap or Siddhi Tapa) is a special form of penance or austerity. It is a 13-day long fast. The practitioner observes austerity for 13 consecutive days, often with certain restrictions on food and sometimes complete fasting, depending on the individual's capacity and the guidance of a Jain monk or nun.

The Sidhi Tap is considered a highly meritorious and rigorous austerity, believed to help in spiritual purification and advancement on the path toward liberation (moksha). It is usually undertaken with great devotion and discipline.