A money manager and

Forbes

columnist who earned a wide following for his staunchly bearish stance over the last few years has changed his tune and is now advising clients to plow 100% of their investment money into stocks.

Ken Fisher, head of the $12 billion Fisher Investment fund and a Forbes columnist since 1984, sent a letter to clients Monday saying it's time to buy.

That's a change from the 0% net equity allocations strategy Fisher's held since 2000 that consisted of a combination of longs, shorts and index puts.

"This might be a material bear market double-bottom," in other words, the start of an uptrend, wrote Fisher. "At the same time, the levels of oversold-ness in today's market is perfectly consistent with any major bottom."

Fisher told clients that the major global equity markets could see a 20% bump over about five months.

His change of heart, which came shortly after he wrote a bearish article for this month's Forbes magazine, caught many of his followers by surprise. In the Forbes story, Fisher was particularly down on technology.

"

Applied Materials

(AMAT) - Get Report

makes wafer fabrication equipment. I think it will be dog meat the rest of this year," he wrote in

Forbes

.

On Tuesday, Applied Materials

posted sales and earnings that were well ahead of expectations, and it noted signs of a recovery in the semiconductor industry. But Fisher said that wasn't the catalyst for his new bullishness.

In an interview Thursday, Fisher said he made the change in his portfolio strategy after analyzing supply and demand in the market and noting an increase in demand. Fisher said he got the information after a cruise from which he wrote the

Forbes

piece. When he got off the cruise, the article had been sent, but Fisher said the information about the markets had changed.

"I had not appreciated the extent that the market was oversold," Fisher said.

In particular, Fisher said he's now overweighted in the technology sector and in U.S.-based equities, as opposed to equities based "in the rest of the world."

"I look at demand and it's too low for the technology sector right now," he said, adding that he's neutral to the other sectors.

But Fisher went on to write in his letter to investors that this may not be a "material bear market bottom. It may be that this is the beginning of a good-sized rally lasting from four to 18 months.

"As we move forward and the market rises, do we move into a period when demand becomes too high or does the market rise on a little increase in demand? It's the demand that will be the indicator," as to whether this is a pop in a bear market or a new bull market, Fisher said.

In his letter, Fisher told his clients that buying conditions now are right, whether it's the beginning of a short- or long-term rally, but he warned, "we may have to later abort our equity positions -- perhaps even before they reach long-term status. We will just have to play it as it comes at us, month-to-month, if need be."

Among those who were struck by Fisher's abrupt reversal were Frank Iryami, a vice president of investments for Salomon Smith Barney. He noted the stark differences in the views Fisher expressed in the recent

Forbes

and in his letter to clients. For his part, Iryami says any upswing simply will be a bear market rally.

"In my opinion, the tech sector is not going to lead the way out. If anything, we may be embarking on a bear rally on tech," he said. "The big money is just not there to push these stocks through because there is no reason to. Companies are still overvalued."