By Angela Chen 

Sprint Corp. Chief Executive Marcelo Claure purchased more than 5 million shares of his company's stock this week, less than a month after the company reported weak full-year results amid struggles to keep customers.

Shares of Sprint jumped on the news, recently rising 6.8% to $5.10 in midday trading. The stock has fallen about 41% over the past 12 months.

Mr. Claure paid about $25 million for the 5.08 million shares, purchased at an average price of $4.92 in separate transactions Wednesday and Thursday, according to a regulatory filing Friday. Mr. Claure joined the company in August after serving on the board since January 2014.

Sprint, which was bought by Japanese technology conglomerate SoftBank Corp. in 2013, has found itself struggling in third place in the U.S. market. It lost 205,000 mainstream "postpaid" cellphone customers in the final three months of the year, booked a higher monthly customer loss rate and wrote down the value of its trademark by $1.9 billion. The results extended a streak of customer losses, and revenue declined 1.8% over the past year.

However, the size of the losses is shrinking. And while its free cash flow--the cash produced by its operations minus capital expenditures--was a negative $1.8 billion last year, that was about $1 billion smaller than its deficit in the year-earlier quarter. The carrier predicted earnings before some adjustments--a figure it previously thought could be flat--would grow between 5% and 7% in 2015.

Write to Angela Chen at angela.chen@dowjones.com

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