The U.S. could be issuing 50-year bonds as soon as next year as the government looks for cheaper and longer-term ways to finance its burgeoning debt load, Treasury Secretary Steven Mnuchin told CNBC on Thursday.

"This is something I have talked about over the last two years, it is something we are very seriously considering," he said on "Squawk Box." "We're looking at issuing a 50-year bond, what we could call an ultra-long bond. We think there is some demand for it. It is something we'll very seriously consider for next year."

Mnunchin's comments come a day after President Donald Trump tweeted that he thinks the U.S. should look at "refinancing" its debt load, which has recently eclipsed the $22.5 trillion mark. Government bond yields moved lower as Mnuchin spoke.

Though it's unlikely the government could engage in that process the way a homeowner would refinance a mortgage, Treasury could extend the maturity of the debt by issuing longer-term bonds. The longest duration the government has now is the 30-year bond.

More than a dozen other developed countries have issued "ultra" bonds of durations from 40 to 100 years. Canada issued a 50-year bond in 2014 while Mexico, Belgium and Ireland have offered 100-year debt in recent years. Multiple companies also have issued 100-year bonds.