The Singapore Exchange came out tops among 664 listed companies to emerge as Singapore's most well-governed and transparent company, according to the latest Governance and Transparency Index (GTI) released on Thursday.

The bourse pipped telco giant SingTel, which had ranked first on the GTI since its launch in 2009, by one point.

Rounding out the top five were Keppel Corporation, Sembcorp Industries and Keppel Land.

Media group Singapore Press Holdings was ranked 15th in a three-way tie with Keppel Telecommunications & Transportation and Neptune Orient Lines.

Most companies improved on their GTI scores in the latest ranking. The 2013 index, released at the CPA Forum, showed that mean scores rose to their highest ever at 38 points, up from 34.9 last year.

But about one-third of listed firms here fell behind last year's scores due to insufficient, inadequate and untimely disclosure.

Companies that end up at the bottom of the list typically cite cost of compliance as the main reason for the lack of disclosure, said Associate Professor Lawrence Loh, the GTI project leader at the NUS Business School.

The GTI is a collaboration between CPA Australia, the NUS Business School's Centre for Governance, Institutions and Organisations, and The Business Times.

The index measures companies based on four key areas: board matters, remuneration, accountability and audit as well as transparency and investor relations. Additional points may be awarded or deducted for good corporate governance practices. The maximum GTI score is 143.

The chairman of the Accounting and Corporate Regulatory Authority (ACRA), Ms Lim Soo Hoon, said: "Setting the right tone at the top is crucial in providing effective governance and inculcating a spirit of accountability."

She urged directors, chief executives and chief financial officers to set the standard for integrity and ethical behaviour among the officers of the company.