Electronics retailer JB Hi-Fi's underlying first-half net profit has jumped by 21 per cent to $151.7 million.

It is anticipating full-year profit to be in the $235-$240 million range — beating its $172 million result last year.

Despite that, its share price plunged by more than 8 per cent to $25.84 at 12:40pm AEDT.

JB Hi-Fi warned that its annual profits would grow at a slower pace than its sales, indicating tighter margins.

In a statement to the ASX, the company said it was expecting its "focus on sales and market share, and continuing changes to sales mix, to result in sales growth exceeding gross profit dollar growth" in the second half of the current financial year.

What's behind the results?

Its profit results were boosted by a healthy Christmas sales period, and its takeover of electronics rival The Good Guys.

But when the costs of The Good Guys acquisition (incurred in the previous half-year period) are included, JB's statutory profit increased by 37.4 per cent.

As for the numbers behind JB Hi-Fi's profit result, sales rose 41 per cent (to $3.7 billion), and pre-tax earnings lifted 25 per cent (to $226 million).

Online sales, in particular, were a particularly strong growth area, surging 40.6 per cent to $119.3 million.

However, there was some weakness in the company's results — particularly from its New Zealand business.

Total sales in New Zealand dropped 0.4 per cent to $115.5 million ($NZ124.6 million).

JB Hi-Fi closed one of its New Zealand stores in the six months ending December 31, while opening seven new stores in Australia.

It now has a total of 311 retail stores across Australia and New Zealand.

In addition, sales from The Good Guys totalled $1.1 billion for the six months to the end of December.

"Having owned The Good Guys for over 12 months we are now starting to realise the benefits of scale of the combined group and remain excited by the opportunity to grow Australia's leading retail brands," JB Hi-Fi's CEO Richard Murray said.

JB Hi-Fi has increased its interim dividend by 19.4 per cent to 86 cents per share, fully franked.