"Our standing depends on the strength of our systems and the reputation of our integrity agencies," he said.
"This is testament to the hard work of our public sector and to the oversight bodies that hold government to account when it is needed."
New Zealand's continued high performance was good for its international reputation, trade, and investment, Boshier said.
The 2020 index ranked 180 countries and territories by their perceived levels of public sector corruption, drawing on expert assessments and surveys.
Denmark and New Zealand received 88 points, while Syria, with 14 points, and Somalia and South Sudan with 12 points each, ranked last.
Transparency International chair Delia Ferreia Rubio said the index revealed widespread corruption was weakening the Covid-19 response.
"Covid-19 is not just a health and economic crisis. It is a corruption crisis. And one that we are currently failing to manage," Rubio said.
"The past year has tested governments like no other in memory, and those with higher levels of corruption have been less able to meet the challenge.
"But even those at the top of the Corruption Perceptions Index must urgently address their role in perpetuating corruption at home and abroad."
