Fifteen Non-Consultant Hospital Doctors each received overtime payments of over €100,000 in 2020, with one working up overtime of over €134,000, according to Freedom of Information documents released by the HSE.
The figures show that the HSE spent €142.7m on overtime for doctors, nurses and midwives last year.
Unions representing doctors and nurses warned that the high levels of overtime disclosed in the figures reflected a serious problem of understaffing in the health service.
However, the HSE stressed that increased absences and service demands triggered by the pandemic had significantly impacted on the requirement for overtime in 2020.
The highest-paid Non-Consultant Hospital Doctor (NCHD) was a Specialist Registrar based in Cork, who earned €213,026 when their overtime of €134,017 was added to basic pay of €79,008.
Another Cork-based Registrar received overtime payments of €120,255 bringing their total pay to €183,934.
Meanwhile, a Galway-based NCHD earned a total pay of €222,050 last year, which included overtime pay of €120,189.
Five other NCHDs received overtime payments between €110,000 and €120,000, with a further seven bringing in overtime ranging from €100,000 to €110,000.
Twenty-one NCHDs earned more in overtime than they made in basic pay.
Meanwhile, the figures released to journalist Gordon Deegan reveal that one Clinical Nurse/Midwife Manager more than doubled their annual pay of €61,331 with overtime of €77,556, bringing their annual earnings to €138,887.
Three other nurses of Clinical Nurse/Midwife Manager grade also earned over twice their basic pay due to overtime ranging from €73,416 to €59,757.
The HSE's total 2020 overtime bill for all NCHDs came to €108.4 million, an increase of 7% on 2019.
Over the same 12-month period, the overtime bill for nurses and midwives rose by 11% to €34.3 million.
In a statement, the HSE noted that overtime hours were generally used to cover short-term absences and/or to respond to immediate service pressures.
It said: "However it is important to note that increased absences and service demands resulting from the Covid-19 pandemic have significantly impacted on the requirement for overtime utilisation in 2020."
The HSE said overtime costs in Mental Health were driven largely by the requirement to maintain rostering levels at safe levels, particularly in acute units and community services.
It acknowledged significant vacancies in the service had been compounded by the impact of the pandemic on staffing levels, particularly as the demand for skilled staff outstripped supply, despite local and international recruitment campaigns.
However, the Irish Medical Organisation said it should be a matter of concern that exhausted doctors were being asked to lead the fight against the pandemic.
"To receive the level of overtime of the top ten earners listed, it would require even the most senior Non Consultant Hospital Doctors in Ireland to work over 70 hours a week every week of the year." said an IMO spokesperson.
"This is an unacceptable situation and runs counter to professed HSE policy on NCHD working hours. It also runs counter to Irish and European Union laws which require employers to ensure their employees do not work on average more than 48 hours a week."
He confirmed the IMO would assist members in taking cases in relation to the rights regarding excessive working hours.
General Secretary of the Irish Nurses and Midwives Organisation Phil Ní Sheaghdha said that even before the pandemic, the health service had relied heavily on overtime and agency staff, adding that at a time when it was "all hands on deck", it was no surprise that the overtime bill had grown again.
She said the government's "misguided" policy up to last March of imposing a HSE recruitment freeze must never be repeated, and called for the recruitment of additional staff and additional safety measures to keep frontline personnel safe.
"Relying on staff to go beyond their hours is not a proper solution - for staff or patients," she warned.
Sinn Féin Health spokesman David Cullinane TD said the overtime figures reflected chronic understaffing on the ground, and the additional strains brought by the pandemic.
He accused the HSE of squeezing more and more out an already overworked workforce, and said the best reward that could be given to healthcare workers would be a normal working week.