There are now plans to recruit 1,000 additional staff to ensure patient care will “continue” being provided.
More than £6.3 million was paid to paramedics to work extra shifts in 2017, official Scottish Ambulance Service figures show.
This marks an increase of £670,000 in a year, and is the highest figure in the past five years.
The organisation spent almost £11.8 million on overtime payments throughout 2017 to all staff, including managers, support staff and technicians, according to data obtained by the Conservatives through Freedom of Information inquiries.
Ambulance chiefs pointed to increasing demand for the service, with a growing and ageing population, while ministers said funding for the organisation is at record levels.
It comes after it emerged last week that staff in Edinburgh’s ambulance call centre are taking an average of three weeks off a year on sick leave.
Scottish Conservative public health spokeswoman Annie Wells said: “Ambulance staff are under huge pressure, and that is increasing according to these figures.
“The fact more than £6m was spent on overtime just for paramedics last year goes to show just how short-staffed the organisation must be.
“Many staff will be willing to do these additional shifts, but from a health and safety perspective, it’s not ideal to be relying on this so heavily.”
She welcomed ongoing work to train a significant number of extra paramedics but added: “Clearly years of under-funding and shambolic workforce planning by the SNP government has contributed to this current unacceptable situation.”
The festive season is a particularly busy time for ambulance workers who contended with “Black Friday” last week as festive revellers contribute to one of their busiest days of the year.
Overtime payments made to ambulance drivers have also doubled since 2013, reaching £38,000 last year.
The rise comes as the Scottish Ambulance Service finds itself under more pressure dealing with an increasing and ageing population, and worsening “turnaround” times at Scotland’s major emergency departments.
Staff sickness absence levels remain considerably higher than the national average, while paramedics face constant antisocial behaviour while attending 999 calls.
In the summer, more than 2500 addresses across the country were “red-flagged” – a policy where ambulance staff aren’t allowed to attend without a police presence.
A Scottish Ambulance Service spokesman said: “All of our staff do a fantastic job helping patients in communities right across Scotland. It is down to their hard work, commitment and professionalism that so many lives are being saved each and every day.”
A Scottish Government spokeswoman said: “We value the tremendous job our ambulance service staff do in what can be exceptionally challenging circumstances. Our ambulance service continues to be one of the best performing services in the UK.”