The stock opened 5.7% above its initial public offering (IPO) price of 875 rupiah a share on the Indonesian stock exchange, before dropping as much as 6.9% to 815 rupiah a share.

The weak debut could weigh on sentiment surrounding upcoming IPOs in Indonesia this year. Pertamina Geothermal's parent Pertamina is also planning an IPO of its upstream unit Pertamina Hulu Energy.

Indonesian state-owned fertiliser company Pupuk Kalimantan Timur has plans for an IPO that could raise $500 million this year, Reuters reported last month, citing sources.

Pertamina Geothermal's IPO was the largest in Indonesia in almost a year after the $1.1 billion listing of tech firm GoTo in April. GoTo has also not done well, share performance wise, with share prices having fallen more than 60% since IPO.

Pertamina Geothermal sold 10.35 billion shares, or 25% of enlarged share capital, and planned to use most of the IPO proceeds to expand capacity of its working geothermal areas, according to its IPO prospectus.

The IPO comes as Pertamina aims to double its geothermal capacity by 2027-2028, which may cost an estimated $4 billion. Indonesia, Southeast Asia's largest economy, is keen to tap into its geothermal resources to cut energy imports and reduce carbon emissions.

($1 = 15,215.0000 rupiah)

(Reporting by Yantoultra Ngui; Editing by Christopher Cushing)